The present invention relates to a drive IC chip for driving a plurality of printing elements provided on a printhead. It also relates to such a printhead.
FIG. 8 schematically shows an example of structure of a thermal printhead. The thermal printhead includes a substrate 91 on which a plurality of heating elements 90 and a plurality of drive IC chips 92 are provided in a respective array. Each of the drive IC chips 92 has a built-in integrated circuit (not shown) for selectively driving the plurality of heating elements 90. When printing data are transmitted from the outside to the integrated circuit, the plurality of heating elements 90 are selectively heated in accordance with the data. Such heating causes printing of an image on a recording paper such as a thermosensitive paper.
FIG. 9 illustrates the structure of the prior art drive IC chip 92. The drive IC chip 92 has a rectangular primary surface 92a which is provided with a plurality of wire-bonding pads 92. The plurality of pads 93 are utilized for electrically connecting the built-in integrated circuit of the drive IC chip 92 to the plurality of heating elements 90, or for supplying power or various signals necessary to drive the integrated circuit. The plurality of pads 93 are arranged along edges 97a, 97b extending widthwise of the primary surface 92a and/or edges 97c, 97d extending lengthwise of the primary surface 92a. In FIG. 9 and any subsequent figures, the direction of a arrow xxe2x80x2 is defined as the lengthwise direction, whereas the direction of an arrow yxe2x80x2 is defined as the widthwise direction.
A single drive IC chip 92 controls, for example, 64 heating elements 90. Assuming that the thermal printhead shown in FIG. 8 provides a printing density of 200 dpi (8 dots/mm) and a maximum printing width of A4 size, the total number of the heating elements 90 is 1728. In this case, the thermal printhead carries a total of 27 drive IC chips 92 suitably arranged at an appropriate interval L.
The prior art described above has the following problems.
In use, two pads 93a, 93b, for example, of each drive IC chip 92 are wire-bonded to pads 96a, 96b, respectively, on the substrate 91, as shown in FIG. 10. The pads 96a, 96b are preferably arranged between two adjacent drive IC chips 92 for allowing two wires W from the respective pads 93a, 93b to extend in the lengthwise direction. If the two wires W from the pads 93a, 93b extend in the widthwise direction as shown in FIG. 11, the wires W become too close to each other because the two pads 93a, 93b overlap each other in the lengthwise direction. This is not preferable for avoiding shorting.
In practically manufacturing a thermal printhead, however, it may be sometimes impossible to extend the wires W in the lengthwise direction. For instance, a larger number of heating elements 90 and drive IC chips 92 need to be used to increase the printing density of a thermal printhead beyond 200 dpi. Accordingly, as shown in FIG. 11, the distance L1 between adjacent drive IC chips 92 becomes smaller than the distance L, so that it may be difficult to dispose the pads 96a, 96b at a narrow region between the drive IC chips 92. Even if the pads 96a, 96b can be disposed between the drive IC chips 92, difficulty may arise in wire-bonding to the pads. In such a case, the wires W need to be extended from the pads 93a, 93b in the widthwise direction as shown in FIG. 11, which is not preferable to prevent shorting between the wires W.
In this way, according to the prior art described above, only one direction is preferred for extending a wire from a pad. A drive IC chip, which is suitable for use in a thermal printhead having a smaller printing density, is not suitable for use in a thermal printhead having a larger printing density because the wire-extending direction needs to be changed. Such a limitation on the wire-extending direction leads to a limitation on the freedom of design with respect to the wiring pattern on the substrate which carries the drive IC chip.
It is, therefore, an object of the present invention to provide a drive IC chip and a printhead which eliminate or lessen the problems described above.
In accordance with a first aspect of the present invention, there is provided a drive IC chip comprising: a built-in integrated circuit for selectively driving a plurality of printing elements of a printhead; a primary surface including at least one first edge extending in a first direction, and at least one second edge extending in a second direction transverse to the first direction; a first and a second pads provided on the primary surface in electrical connection to the integrated circuit; wherein the first and the second pads are provided at a corner at which the first and the second edges meet; and wherein respective centers of the first and the second pads deviate positionally from each other in the first and the second directions.
With the drive IC chip having such a structure, wires may be bonded to the first and the second pads at respective portions which deviates positionally from each other in the first and the second directions. Accordingly, regardless of whether the wires are extended in the first direction or in the second direction, the wires can be appropriately spaced from each other to reduce the likelihood of shorting between the wires. Further, since the first and the second pads are provided at a common corner of the primary surface, the wires can be readily extended out of the drive IC chip, regardless of whether the wires are extended in the first direction or in the second direction.
According to the present invention, in this way, there is no great limitation on the extending direction of the wires which are connected to the first and the second pads. Thus, the present invention is applicable both where wires can be extended toward a region between adjacent drive IC chips, and where such wire-extension is impossible. Further, since the wire extending direction is selectable, there will be greater freedom in designing the wiring patterns for the substrate on which the drive IC chips are mounted.
Preferably, each of the first and the second pads may be used either for supplying power for driving the integrated circuit, or for grounding the integrated circuit, or for inputting/outputting signals to the integrated circuit.
Preferably, the first and the second pads may be held entirely out of overlapping relation with each other both in the first and the second directions. Such an arrangement make it is possible to more reliably prevent the wires connected to the first and the second wires, respectively, from becoming too close to or contacting each other.
Preferably, the first pad may be rectangular to be elongate in the first direction, whereas the second pad may be rectangular to be elongate in the second direction. With such a structure, it is possible to bond wires to the first and the second pads at respective positions which are offset from respective centers of the pads longitudinally thereof. As a result, the distance between the wires can be increased, which is advantageous in preventing the wires from contacting.
Preferably, the first pad may be provided at the first edge, whereas the second pad may be provided at the second edge. With such a structure, it is possible to arrange the first and the second pads at the corner of the primary surface in a space-efficient manner, thereby decreasing waste of space at the corner.
Preferably, the primary surface may be rectangular to have a pair of first edges, a pair of second edges, and four corners.
Preferably, the drive IC chip may further include a plurality of third pads for electrically connecting the integrated circuit to the plurality of printing elements, and the third pads be arranged along one of the paired second edges.
Preferably, the first and the second pads are provided at one of the four corners which is close to the other of the paired second edges. Such an arrangement enables the first and the second pads to be kept away from the plurality of third pads as much as possible in a space-efficient manner.
In accordance with a second aspect of the present invention, there is provided a printhead comprising a substrate provided with a plurality of printing elements arranged in a row, and a plurality of drive IC chips; each of the drive IC chips comprising: a built-in integrated circuit for selectively driving the plurality of printing elements; a primary surface including at least one first edge extending in a first direction, and at least one second edge extending in a second direction transverse to the first direction; a first and a second pads provided on the primary surface in electrical connection to the integrated circuit; wherein the first and the second pads are provided at a corner at which the first and the second edges meet; and wherein respective centers of the first and the second pads deviate positionally each other in the first and the second directions.
Preferably, the printing elements are heating elements.
The printhead having such a structure enjoys the same advantages as the drive IC chip provided in accordance the first aspect of the present invention.
Other features and advantages of the present invention will become clearer from the description of embodiments given below.